1. Field of the Invention
The present invention relates to a stage apparatus that is suitable for performing precision positioning. More specifically, the present invention relates to a stage apparatus that is used for a semiconductor exposure apparatus and, on which a wafer, or the like, is mounted. More specifically, the present invention relates to an exposure apparatus that uses such a stage apparatus, and relates to a device manufacturing method for manufacturing a device, such as a semiconductor device, by using such an exposure apparatus.
2. Description of the Related Art
For an exposure apparatus used for manufacturing a device, such as a semiconductor device, a step-and-repeat type exposure apparatus (also referred to as a stepper), or a step-and-scan type exposure apparatus (also referred to as a scanner), is typically used. A step-and-repeat type exposure apparatus moves a substrate (such as wafer and a glass substrate) in stepped movements, so that an original plate (such as a reticle and a mask) pattern can be projected through a projection optical system, and sequentially exposed onto a plurality of exposure areas on the substrate. A step-and-scan type exposure apparatus repeats exposure and transfer on a plurality of exposure areas on a substrate by repeating a step movement and a scanning exposure. In a step-and-scan type exposure apparatus, in particular, exposure light used is limited to a portion relatively near the optical axis of the projection optical system because of a slit. Thus, it is possible to expose a minute pattern precisely and with a wide angle of field.
FIG. 1 is an illustration that shows a schematic structure of a typical exposure apparatus. A base 105 is supported on anti-vibration units 106 on a floor F, and a wafer stage 104, which is movable in two-dimensional directions (directions X and Y), is supported on the base 105. A projection optical system 103 is supported above the wafer stage 104 and a reticle stage 102 is supported further above, with a main body supporting component (not shown). The reticle stage 102 supports a reticle R, and a lighting system 101 for supplying an exposure light is positioned above the reticle stage 102.
In the structure explained above, the wafer stage 104, which has a wafer W, which has been supplied with a wafer transfer system (not shown), mounted on it, is moved on the base 105 in the directions X and Y by an XY driving mechanism (not shown). In an exposure operation, the wafer stage 104 is moved by the XY driving mechanism so that the wafer W is positioned at a target position (exposure location) with respect to the reticle R. After completion of positioning, an image of the reticle R is printed on the wafer W. When printing is complete, the wafer stage 104 is driven so that the next exposure location of the wafer W can be exposed. An exposure apparatus in FIG. 1 prints reticle images on the single wafer W in its entirety, by repeating the above-mentioned steps.
In an exposure apparatus mentioned above, it is necessary to shorten the time required for moving and the time required for exposing the wafer stage 104, to improve productivity. In order to shorten the time required for moving the wafer stage 104, the acceleration and deceleration during movement must be increased. Meanwhile, the diameter of the wafer W needs to be increased to improve productivity of the post process steps, which is causing a growing increase in the mass of a wafer chuck and of the wafer stage 104.
In such an exposure apparatus, when a stage is driven, a reaction force of an inertia force is generated as the stage accelerates and decelerates, and if the reaction force is transferred to the base 105, the base 105 can vibrate. Such vibrations may prevent high-speed and precise positioning, since they may excite natural oscillation of the mechanism of the exposure apparatus and cause high-frequency oscillation. For this reason, several proposals have been made so that issues related to such a reaction force can be solved. For example, an apparatus described in Japanese Laid-Open Publication No. H5-77126A prevents a reaction force from causing vibration of a stage base by having a stator of a linear motor for driving the stage supported on the floor independently of the stage base. In an apparatus described in Japanese Laid-Open Publication No. H5-121294A, vibrations of the apparatus caused by a reaction force are reduced by providing a machine frame that supports a wafer stage and a projection lens with a compensating force that is equivalent to the reaction force generated when the stage is driven, using the force of the actuator generated in the horizontal direction.
However, in both of the above-mentioned conventional methods, although vibrations of the stage apparatus itself can be reduced, the reaction force generated when the stage is driven is transferred directly to the floor or transferred to the floor through a component that can be practically regarded as being integrated with the floor. This can vibrate the floor, which can vibrate and give adverse impacts on devices installed near the exposure apparatus. Generally, floors on which an exposure apparatus is installed have a natural frequency in the approximate range of 20 to 40 Hz. If an operation of the exposure apparatus excites vibrations in the natural frequency of the floor, there will be a significant adverse impact on the devices nearby.
In these days, acceleration of the stage has been increasing as the throughput speed improves, and, furthermore, mass of the stage has been increasing as reticles and substrates become larger. In response to this, the driving force, which is calculated by multiplying “mass of the moving unit” by “acceleration,” has become significantly large with its reaction force, also to become enormous. As the reaction force increases, the issue of vibrations that the reaction force apply to the installation floor must be addressed.
In addition, increases in the size of the apparatus are notable, and the issue of increases in the area required for installation, within a manufacturing plant in which numerous manufacturing devices are installed, has started to manifest. Furthermore, if vibrations transferred to the floor from an apparatus, as mentioned above, are large, it is necessary to assure a larger distance between devices to prevent effects of vibrations from being transferred to other devices. Upsizing of the apparatus and security of a distance between devices cause a significant increase in the area practically occupied by each of the devices.
Although the anti-vibration units 106 are typically provided between the floor F and the base 105, it is impossible to avoid transfer to the floor of the reaction force, which is generated when the stage 104 is driven, with a conventional device for receiving reaction forces. For example, the moments around the X axis and the Y axis generated when the wafer stage 104 moves within the XY plane are transferred to the floor F.
As shown in FIG. 2, a structure that reduces transfer of vibrations to a floor F by combining anti-vibration units 106 and a post 221 has been proposed. In FIG. 2, transfer of the vibrations of a base 105 to the floor F is reduced by providing the anti-vibration units 106 between the base 105 and the floor F, and fixing the floor F and the base 105 through the post 221. However, even with such a structure, it is impossible to avoid transfer to the floor F of the reaction force that is generated when the stage is driven.
As shown in FIG. 2, when a wafer stage 104 with a mass of m moves at an acceleration of a, an internal force m·a in a plane and a moment force M=L·m·a acts on the floor face. The value L represents the distance between the position of the center of gravity of the movable stage and the floor face. In general, since the floor face has a high stiffness against the internal force in a plane, but has a low stiffness against the moment force, the above-mentioned moment force: M=L·m·a causes the floor to vibrate. The vibrations of the floor have adverse effects on the apparatus itself and the surrounding devices.
For a driving device in which the center of gravity of the base that supports the stage does not match the center of gravity of the stage, the applicant of the present invention considers it effective to provide a driving device with a reaction force counter that reduces the force transferred outside. However, even in an apparatus to which the reaction force counter is provided, unless the center of gravity of the stage and that of the base match each other on the YZ plane or on the ZX plane, moments are generated around the X axis or around the Y axis, and they are transferred to the floor.
For a driving device in which the center of gravity of the base that supports the stage does not match the center of gravity of the stage, a device described in Japanese Laid-Open Publication No. H11-190786A uses a rotating body as a method for reducing or canceling out the moments generated when the stage moves.
The use of a rotating body, however, requires an installation area equivalent to the diameter of the rotating body, both in the direction Y and in the direction Z, of the YZ plane for when the moment is generated around the X axis. For this reason, when a rotating body is installed to a space limited in either of the directions, there is a limit to the diameter of the rotating body. In this case, required moments must be generated with a rotating body with a small diameter. In order to generate a large moment with a rotating body with a small diameter, the rotating speed becomes significantly high, since a small moment of inertia requires a large angular acceleration. In general, motor speed is limited, and if a large current is used to achieve high-speed revolution with a motor with a small volume, heat generation becomes large as well. Furthermore, there is also an issue of high frequency oscillation during high-speed revolution if the center of gravity of the rotating body does not completely match the rotating axis.